211 research outputs found
Gene knockouts reveal separate functions for two cytoplasmic dyneins in Tetrahymena thermophila
In many organisms, there are multiple isoforms of cytoplasmic dynein heavy chains, and division of labor among the isoforms would provide a mechanism to regulate dynein function. The targeted disruption of somatic genes in Tetrahymena thermophila presents the opportunity to determine the contributions of individual dynein isoforms in a single cell that expresses multiple dynein heavy chain genes. Substantial portions of two Tetrahymena cytoplasmic dynein heavy chain genes were cloned, and their motor domains were sequenced. Tetrahymena DYH1 encodes the ubiquitous cytoplasmic dynein Dyh1, and DYH2 encodes a second cytoplasmic dynein isoform, Dyh2. The disruption of DYH1, but not DYH2, resulted in cells with two detectable defects: 1) phagocytic activity was inhibited, and 2) the cells failed to distribute their chromosomes correctly during micronuclear mitosis. In contrast, the disruption of DYH2 resulted in a loss of regulation of cell size and cell shape and in the apparent inability of the cells to repair their cortical cytoskeletons. We conclude that the two dyneins perform separate tasks in Tetrahymena
Towards Space-like Photometric Precision from the Ground with Beam-Shaping Diffusers
We demonstrate a path to hitherto unachievable differential photometric
precisions from the ground, both in the optical and near-infrared (NIR), using
custom-fabricated beam-shaping diffusers produced using specialized
nanofabrication techniques. Such diffusers mold the focal plane image of a star
into a broad and stable top-hat shape, minimizing photometric errors due to
non-uniform pixel response, atmospheric seeing effects, imperfect guiding, and
telescope-induced variable aberrations seen in defocusing. This PSF reshaping
significantly increases the achievable dynamic range of our observations,
increasing our observing efficiency and thus better averages over
scintillation. Diffusers work in both collimated and converging beams. We
present diffuser-assisted optical observations demonstrating
ppm precision in 30 minute bins on a nearby bright star
16-Cygni A (V=5.95) using the ARC 3.5m telescope---within a factor of 2
of Kepler's photometric precision on the same star. We also show a transit of
WASP-85-Ab (V=11.2) and TRES-3b (V=12.4), where the residuals bin down to
ppm in 30 minute bins for WASP-85-Ab---a factor of 4 of
the precision achieved by the K2 mission on this target---and to 101ppm for
TRES-3b. In the NIR, where diffusers may provide even more significant
improvements over the current state of the art, our preliminary tests have
demonstrated ppm precision for a star on the 200"
Hale Telescope. These photometric precisions match or surpass the expected
photometric precisions of TESS for the same magnitude range. This technology is
inexpensive, scalable, easily adaptable, and can have an important and
immediate impact on the observations of transits and secondary eclipses of
exoplanets.Comment: Accepted for publication in ApJ. 30 pages, 20 figure
TOI-3785 b: A Low-Density Neptune Orbiting an M2-Dwarf Star
Using both ground-based transit photometry and high-precision radial velocity
(RV) spectroscopy, we confirm the planetary nature of TOI-3785 b. This
transiting Neptune orbits an M2-Dwarf star with a period of ~4.67 days, a
planetary radius of 5.14 +/- 0.16 Earth Radii, a mass of 14.95 +4.10, -3.92
Earth Masses, and a density of 0.61 +0.18, -0.17 g/cm^3. TOI-3785 b belongs to
a rare population of Neptunes (4 Earth Radii < Rp < 7 Earth Radii) orbiting
cooler, smaller M-dwarf host stars, of which only ~10 have been confirmed. By
increasing the number of confirmed planets, TOI-3785 b offers an opportunity to
compare similar planets across varying planetary and stellar parameter spaces.
Moreover, with a high transmission spectroscopy metric (TSM) of ~150 combined
with a relatively cool equilibrium temperature of 582 +/- 16 K and an inactive
host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune
targets for atmospheric follow-up. Future investigation into atmospheric mass
loss rates of TOI-3785 b may yield new insights into the atmospheric evolution
of these low-mass gas planets around M-dwarfs.Comment: 22 pages, 6 figures, 6 tables, Submitted to A
lpxC and yafS are the Most Suitable Internal Controls to Normalize Real Time RT-qPCR Expression in the Phytopathogenic Bacteria Dickeya dadantii
Background: Quantitative RT-PCR is the method of choice for studying, with both sensitivity and accuracy, the expression of genes. A reliable normalization of the data, using several reference genes, is critical for an accurate quantification of gene expression. Here, we propose a set of reference genes, of the phytopathogenic bacteria Dickeya dadantii and Pectobacterium atrosepticum, which are stable in a wide range of growth conditions. [br/]
Results: We extracted, from a D. dadantii micro-array transcript profile dataset comprising thirty-two different growth conditions, an initial set of 49 expressed genes with very low variation in gene expression. Out of these, we retained 10 genes representing different functional categories, different levels of expression (low, medium, and high) and with no systematic variation in expression correlating with growth conditions. We measured the expression of these reference gene candidates using quantitative RT-PCR in 50 different experimental conditions, mimicking the environment encountered by the bacteria in their host and directly during the infection process in planta. The two most stable genes (ABF-0017965 (lpxC) and ABF-0020529 (yafS) were successfully used for normalization of RT-qPCR data. Finally, we demonstrated that the ortholog of lpxC and yafS in Pectobacterium atrosepticum also showed stable expression in diverse growth conditions. [br/]
Conclusions: We have identified at least two genes, lpxC (ABF-0017965) and yafS (ABF-0020509), whose expressions are stable in a wide range of growth conditions and during infection. Thus, these genes are considered suitable for use as reference genes for the normalization of real-time RT-qPCR data of the two main pectinolytic phytopathogenic bacteria D. dadantii and P. atrosepticum and, probably, of other Enterobacteriaceae. Moreover, we defined general criteria to select good reference genes in bacteria
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b
Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600â800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44 ± 0.12 R_â and 24.5_(-5.2)^(+5.7) M_â. These properties are compatible with a rocky core enshrouded by a thin hydrogenâhelium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 ± 0.05. The sky-projected stellar obliquity is λ = 3° ± 16°, compatible with spinâorbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars
Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au
Based on two decades of radial velocity (RV) observations using Keck/High Resolution Echelle Spectrometer (HIRES) and McDonald/Tull, and more recent observations using the Automated Planet Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3 minimum mass planet with an orbital period of yr. The orbit is highly eccentric (e â 0.84), shuttling the planet from within the orbit of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled high cadence observations before, during, and after the planet\u27s periastron passage, yielding precise orbital parameter constraints. We searched for stellar or planetary companions that could have excited the planet\u27s eccentricity, but found no candidates, potentially implying that the perturber was ejected from the system. We did identify a bound stellar companion more than 15,000 au from the primary, but reasoned that it is currently too widely separated to have an appreciable effect on HR 5183 b. Because HR 5183 b\u27s wide orbit takes it more than 30 au (1\u27\u27) from its star, we also explored the potential of complimentary studies with direct imaging or stellar astrometry. We found that a Gaia detection is very likely, and that imaging at 10 ÎŒm is a promising avenue. This discovery highlights the value of long-baseline RV surveys for discovering and characterizing long-period, eccentric Jovian planets. This population may offer important insights into the dynamical evolution of planetary systems containing multiple massive planets
The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
Using radial-velocity data from the Habitable-zone Planet Finder, we have
measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity
of its M4.5-dwarf host star in the 600-800MYr Hyades cluster. This is one of
the youngest planetary systems for which both of these quantities have been
measured, and one of the very few M dwarfs with a measured obliquity. Based on
a joint analysis of the radial velocity data, time-series photometry from the
K2 mission, and new transit light curves obtained with diffuser-assisted
photometry, the planet's radius and mass are
and . These properties are compatible
with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass).
We measure an orbital eccentricity of . The sky-projected
stellar obliquity is , compatible with spin-orbit
alignment, in contrast to other "hot Neptunes" that have been studied around
older stars.Comment: Accepted for publication in AJ, 31 pages, 14 figure
TOI-5205b: A Jupiter transiting an M dwarf near the Convective Boundary
We present the discovery of TOI-5205b, a transiting Jovian planet orbiting a
solar metallicity M4V star, which was discovered using TESS photometry and then
confirmed using a combination of precise radial velocities, ground-based
photometry, spectra and speckle imaging. The host star TOI-5205 sits near the
eponymous `Jao gap', which is the transition region between partially and
fully-convective M dwarfs. TOI-5205b has one of the highest mass ratio for M
dwarf planets with a mass ratio of almost 0.3, as it orbits a host star
that is just . Its planetary radius is , while the mass is . Additionally, the large size
of the planet orbiting a small star results in a transit depth of ,
making it one of the deepest transits of a confirmed exoplanet orbiting a
main-sequence star. The large transit depth makes TOI-5205b a compelling target
to probe its atmospheric properties, as a means of tracing the potential
formation pathways. While there have been radial velocity-only discoveries of
giant planets around mid M dwarfs, this is the first transiting Jupiter with a
mass measurement discovered around such a low-mass host star. The high mass of
TOI-5205b stretches conventional theories of planet formation and disk scaling
relations that cannot easily recreate the conditions required to form such
planets.Comment: Submitted to ApJ. Comments are welcome. arXiv admin note: text
overlap with arXiv:2203.0717
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